there's no proof that the tach is broken. I don't buy it, but I'll humor this for a moment.

Assuming he saw 8000 rpm at 100 mph, there's only one transmission that would mathematically allow that, and it's not a B16 trans. It's an Integra LS tranny. Nobody interested in performance would use one of these, except maybe for turbo, but that's not the case here. The speed shown corresponds fairly well to 10k rpm in 3rd gear of an S80 Type R tranny. Stock tachs aren't 100% accurate of course, so it could also be a GSR or B16 trans.